Automatic engine protection: purpose and purpose

The motor protection device is used to protect the windings from short circuit, overload, and also when one of the three phases of the supply circuit is broken. The latter condition occurs when the switching equipment is faulty or the integrity of the cable connecting the boron motor to the relay circuit is broken.

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The motor protection unit is set as the first link in the motor supply network. Further, an electromagnetic starter is located , after which a thermal relay can additionally be used . Modern models have the ability to adjust the cutoff current.

Most often, the types of automata in question are used to protect three-phase motors. Each winding clings to its contact, but the device turns off in all phases. This operating principle distinguishes the device from type B and C switches. Speedy motors start under load under severe conditions. In this case, the starting current often exceeds the nominal value up to 6 times. Conventional switches will work instantly, the automaton will shut down only after a steady increase in the amperage.

Electrical device parameters

The selection of the motor protection starts with the following characteristics:

• Motor operating current.
• The value of the supply voltage.
• Number of windings.
• An important characteristic is the ability of the switch to disconnect the short-circuit current. In conventional machines it does not exceed 6 kA, in the latest versions it exceeds 50 kA. The response time is taken into account: selective - up to 1 s, normal - up to 0.1 s, high-speed - no more than 0.005 s.
• Dimensions. Most machines are connected to the mains via a fixed-line bus. It is often problematic to insert the first switch that is on the other side.
• Type of release mechanism: the possibility of thermal and electromagnetic protection.

Warning of malfunctions of the electric motor

It is important to know not only what protective functions are performed by the motor protection circuit, but also to take into account the technical nuances of the connected electrical circuit. In the case of using high-speed motors, faults can occur when a slightly overcurrent flows through one contact of the switching relay. After a long operation, this will result in the failure of one winding. It will take a more sensitive switch, capable of breaking the circuit when the wire is heated.

Some motors are critical to the short-term loss of one of the feeding phases. Even if an automatic motor protection and thermal protection are used, it will be necessary to install models that turn off when the supply voltage is lost on one of the contacts. Accordingly, such devices have a more complex structure, which affects their cost. Manufacturers strongly do not recommend connecting several power circuits to one device.

Additional properties of switching equipment

The motor protection circuit is designed to operate in a certain range of ambient temperatures. After exceeding the maximum limit set by the manufacturer, false alarms may occur. If the switch is put in a place that is too cold, it will not shut down at the right time at all. Therefore, if necessary, installers will provide appropriate technical compensation.

In the workplace there can be situations when the machine itself is out of order, and the remaining elements remain serviceable. In some models, the protection function on the front panel of the circuit breaker is provided. This is a temporary measure before installing a new device in order to ensure continuous delivery of products. However, there is a risk of damaging an expensive element - the engine.